SPRING AND SUMMER PREY OF 



CALIFORNIA SEA LIONS, ZALOPHUS CALIFORNIANUS, 



AT SAN MIGUEL ISLAND, CALIFORNIA, 1978-79. 



George A. Antonelis, Jr., Clifford H. Fiscus, and Robert L. DeLong 1 



ABSTRACT 



During the late spring and summer of 1978 and 1979, 224 scats were collected from rookeries of the Cali- 

 fornia sea lion, Zalophus californianus , at San Miguel Island for the purpose of identifying prey species. A 

 total of 2,629 otoliths and 2,06 1 cephalopod beaks were recovered. The frequency of occurrence for the four 

 most commonly identified prey species was 48.7% Pacific whiting, Merluccius productus; 46.7% market 

 squid, Loligo opalescens; 35.9% rockfish, Sebastes spp.; and 20.0% northern anchovy, Engraulis mordax. 

 Seasonal variability in the frequency of occurrence of these four prey species from late spring to summer 

 indicates that California sea lions feed opportunistically on seasonally abundant schooling fishes and squids. 

 Five species of fish (California smoothtongue, Bathylagus stilbius; northern lampfish, Stenobrachius leucop- 

 sarus; chub mackerel, Scomber japonicus; medusafish, Icichthys lockingtoni; sablefish, Anoplopoma fimbria) 

 and one cephalopod (two-spotted octopus, Octopus bimaculatus) were identified as previously unreported 

 prey of the California sea lion. 



The California sea lion, Zalophus californianus, is the 

 most abundant pinniped inhabiting the coastal 

 waters off California (Le Boeuf and Bonnell 1980). 

 During the summer most California sea lions are on 

 or near their breeding sites which are located on 

 islands south of Point Conception, along the coast of 

 southern California, Baja California, and into the 

 Gulf of California. After the breeding season in the 

 summer, a portion of the subadult and adult male sea 

 lion populations migrates north of Point Conception 

 as far as British Columbia, while the rest of the pop- 

 ulation remains off the coasts of southern California 

 and Baja California, Mexico (Peterson and Bartho- 

 lomew 1967). Numerous studies of the food of 

 migrant male California sea lions have been con- 

 ducted in the areas north of their traditional breeding 

 islands (Briggs and Davis 1972; Jameson and 

 Kenyon 1977; Morejohn et al. 1978; Bowlby 1981; 

 Everitt et al. 1981; Jones 1981; Ainley et al. 1982; 

 Bailey and Ainley 1982), while comparatively little 

 information has been reported on the feeding 

 behavior of sea lions in areas off the coast of Cali- 

 fornia south of Point Conception (Rutter et al. 1904; 

 Scheffer and Neff 1948; Fiscus and Baines 1966). 

 From the information presented in all of these 

 studies, it has been suggested that California sea 

 lions feed opportunistically on a variety of prey 



species (Antonelis and Fiscus 1 980) and that "switch 

 feeding" is probably an important component of 

 their feeding behavior (Bailey and Ainley 1982). 

 However, since most of the information on sea lion 

 feeding behavior is based on observations north of 

 their breeding islands, additional information from 

 within their breeding range would allow us to deter- 

 mine if similar feeding characteristics can be expect- 

 ed in other geographical areas. 



Studies conducted before 1970 usually obtained 

 stomach contents for feeding information by killing 

 sea lions, while most post- 1970 feeding studies have 

 used nonlethal techniques including examination of 

 scats and oral rejecta (spewings) and direct 

 behavioral observations. Another method was the 

 examination of gastrointestinal tracts from animals 

 found dead. In this study, prey-species classification 

 is based on the identification of fish otoliths and 

 cephalopod beaks found in scats collected during the 

 spring and summer for two consecutive years on the 

 California sea lion rookeries of San Miguel Island, 

 Calif. In addition to the identification of prey, we 

 calculated the percent frequency of occurrence of 

 each prey, compared annual and seasonal differ- 

 ences in prey selection, and estimated the lengths 

 and weights of the most frequently occurring prey 

 species. 



'Northwest and Alaska Fisheries Center National Marine Mammal 

 Laboratory, National Marine Fisheries Service, NOAA, 7600 Sand 

 Point Way N.E., Seattle, WA 98115. 



Manuscript accepted July 1983. 



FISHERY BULLETIN: VOL. 82, NO. 1, 1984. 



MATERIALS AND METHODS 



Scats were collected from areas utilized exclusively 



67 



